1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image (hereinafter, is sometimes simply referred to as xe2x80x9ctonerxe2x80x9d) utilizing an electrophotographic process or an electrostatic recording process, a two-component developer containing the toner, and an image-forming process using the toner.
2. Related Art
Hitherto, in the case of forming images in a copying machine, a laser beam printer, etc., a Carlson process is generally used. In an image-forming process by a black and white electrophotographic process in a conventional art, an electrostatic latent image formed on a photoreceptor by an optical method is developed with a developing step, thereafter, the developed image is transferred to a recording medium such as a recording paper, etc., in a transfer step, and then the transferred image is fixed to the recording medium such as the recording paper, etc., generally by a heat and pressure in a fixing step to obtain a black and white image.
However, in the recent electrophotographic technique, the progress of from black and white to full color has been rapidly progressed. In the color image formation by a full color electrophotographic process, the regeneration of all colors is generally carried out using four-color toners composed of three-color toners of yellow, magenta, and cyan which are the three primary colors added with a black toner. In a general full color electrophotographic process, first, an original is color-separated in yellow, magenta, cyan, and black and per each color, an electrostatic latent image is formed on a photoconductive layer. Then, a toner is held on a recording medium through a development and a transfer step. Then, the above-described steps are successively carried out plural times per each color, and while matching the positions of toner images each having each different color, the toner images each having each different color are overlapped on a same recording medium. Also, by applying one fixing process, a full color image is obtained. The point of overlapping several kinds of toner images each having a different color as described above is a large difference between the black and white electrophotographic process and the full color electrophotographic process. In the color toners used for the full color electrophotographic process, it is necessary that the toners of many colors are sufficiently mixed in the fixing process and by sufficiently mixing these multicolor toners, the color reproducibility and the transparency of an OHP image are improved, and a full color image having a high image quality can be obtained. Thus, as compared with a black toner for black and white print, it is desired that the color toners are generally formed by sharp melting low-molecular weight resin to increase the color mixing property.
In the black toner for the black and white prints of prior art, because the toner image is brought into contact with a fixing unit such as a heat roller, etc., in a heat-melt state, to prevent the occurrence of a so-called offset phenomenon that a part of the toner image attaches and transfers to the surface of the heat roller, the black toner contains therein a wax having a high crystalline property and a relatively high melting point, such as polyethylene, polypropylene, etc. In general, in the case of a high viscous toner such as the black toner for the black and white print, since the intermolecular cohesive force at heat-melting of the toner is strong, the occurrence of the offset phenomenon can be prevented by oozing out a small amount of the wax. However, when it is necessary to color by overlapping toners of two or more colors such as full color toners and to form a flat fixed image surface for giving a transparency of an OHP image, it is required to lower the viscosity of the toners and increase the heat-melting property of the toners. In this case, for obtaining a sufficient effect for the anti-offset property, it is necessary to add a large amount of wax to the toners. However, because in the case of the toners prepared by a melt-kneading/grinding method, the toners become the structures of exposing the wax onto the surfaces of the toners, whereby a large amount of the wax exposed on the surfaces of the toners causes filming to a photoreceptor and is liable to stain the carriers and the surfaces of the developing sleeve, and thus the images formed are liable to be deteriorated.
Accordingly, a method has been employed wherein usually color toners for full color do not contain wax, for the purpose of preventing the occurrence of offset phenomenon, the surface of heat-fixing roller is formed with a silicone rubber or a fluorine resin excellent in the releasing property to the toners and further a releasing liquid such as s silicone oil, etc., is supplied to the surface of the roller. The method is very effective in the point of preventing the occurrence of the offset phenomenons of toners, but there is a problem that an apparatus for supplying an offset preventing liquid becomes necessary. This is not directed to the small sizing and the light weighing of the image-forming apparatus, and also there sometimes occur the problems that the offset preventing liquid is evaporated by heating to give an unpleasant smell and the vapor of the liquid stains the inside of the apparatus.
Therefore, for the color toners for full color, a sharp melting low-molecular resin is used, and the toners contain only a small amount of a low-melting wax and can be fixed without supplying a releasing liquid to the surface of the heat-fixing roller has been investigated.
As one of the investigations, various reports have been made for controlling the molecular weight distribution of binder resins. In general, a resin having a low molecular weight has a low viscosity and is sharp melting and is useful for a low-temperature fixing and the formation of a flat fixed image, but is inferior in the anti-offset property. Also, a resin having a high molecular weight has a high viscosity and is useful for the anti-offset property but is disadvantageous for low-temperature fixing and the formation of a flat fixed image.
Thus, there are many attempts of satisfying both the low-temperature fixing property and the anti-offset property by combining a resin having a low-molecular weight if and a resin having a high-molecular weight, or by defining the molecular weight distribution. For example, as the toner defining the molecular weight distribution, there are a toner defining the value of Mw/Mn as described in Japanese Patent Laid-Open Nos. 284863/1989 and 207126/1998, a toner having the two maximum values as described in Japanese Patent Laid-Open No. 294866/1991, a toner having the three maximum values as described in Japanese Patent Laid-Open Nos. 221758/1989 and 63035/1998, a toner finely defining the ratio of a low molecular weight component and a high molecular weight component as described in Japanese Patent Laid-Open Nos. 44110/1996, 228131/1998, and 278067/1991, and the like.
Because these toners have a low fixing temperature and can improve the anti-offset property, they are sufficient for obtaining monochromatic images. However, because the toners containing a crosslinking component or a high molecular weight component of at least 1xc3x97106 as described in Japanese Patent Laid-Open Nos. 294866/1991 and 221758/1998 do not have a low melt viscosity and cannot form a flat fixed image, the transparency is bad and these toners are insufficient as full color toners.
Also, by the molecular weight distributions having a wide distribution as defined in Japanese Patent Laid-Open Nos. 284863/1989, 44110/1996, 207126/1998, and 228131/1998, the balance of the low molecular weight component and the high molecular weight component is bad and all of the low-temperature fixing property, the OHP transparency, and the flat fixed image forming performance cannot be simultaneously satisfied in sufficiently levels. That is, because the molecular weight distribution having a wide distribution contains large amounts of a low-molecular weight component and a high-molecular weight component, there are problems that the low-molecular weight component lowers the characteristics of the anti-offset property, and the high-molecular weight component lowers the low-temperature fixing property and the flat fixed image forming performance.
Also, the toner disclosed in Japanese Patent Laid-Open 63035/1998 has the peak at the region of a very low molecular weight of from 500 to 1000. Because the toner has a very large amount of a low-molecular weight component, the anti-offset property is insufficient. As a fixing method of solving the problem of the anti-offset property, a method of increasing a pressure at fixing to anchor the toner on a transfer material can be employed, but the separation traces of a member of separating the transfer material from a fixing roller appear on images and further owing to the high pressure, a line image is smashed at fixing, whereby image defects of the copy images are liable to cause.
Also, in Japanese Patent Laid-Open No. 278067/1991, a toner wherein the ratio of the molecular weight distribution of 10,000 or lower is from 55 to 80% is described, but because the toner contains a large amount of a very low-molecular component, fixing without oil is difficult.
The present invention has been made for solving the above-described problems in the techniques. That is, the present invention provides a toner for developing an electrostatic latent image which is excellent in the low-temperature fixing property, the OHP transparency, and the anti-offset property without substantially coating oil in heat roll fixing and can form a fixing image having a high glossiness, a two-component developer containing the toner, and an image-forming process using the toner.
The present invention solving the above-described problems is as follows.
That is, the 1st aspect of the invention is a toner for developing an electrostatic latent image containing a binder resin, a colorant, and a wax. In regard to the molecular weight by GPC of the THF dissolved components of the toner, the ratio of at least 5xc3x97105 in the integral molecular weight distribution is not higher than 1% by weight, the ratio of not higher than 3xc3x97103 in the integral molecular weight distribution is not higher than 30% by weight, and the ratio {W(5xc3x97103)/W(1xc3x97103)} of the ratio {W(5xc3x97103)} of not higher than 5xc3x97103 in the integral molecular weight distribution to the ratio {W(1xc3x97103)} of at least 1xc3x97103 in the integral molecular weight distribution is from 15 to 50.
The 2nd aspect of the invention is also a toner for developing an electrostatic latent image containing at least a binder resin, a colorant, and a wax. The molecular weight by GPC of the THF dissolved components of the toner is distributed in the range of not larger than 1xc3x97106, the value of the differential molecular weight distribution of the molecular weight 5xc3x97103 is not larger than 0.55%, and the value of the differential molecular weight of the molecular weight 1xc3x97105 is not larger than 0.15%.
The 3rd aspect of the invention is a two-component developer containing the toner and carrier, and the toner is described in the above-described 1st or 2nd aspect.
The 4th aspect of the invention is an image-forming process including a latent image-forming step of forming an electrostatic latent image on a latent image holding member, a developing step of forming a toner image by developing the electrostatic latent image with a toner, a transfer step of transferring the toner image onto a transfer material to form a transfer image, and a fixing step of fixing the transferred image using a fixing apparatus comprising, for example, a heat roller and a press roller. The toner is that described in the aspect 1 or 2 above, the surfaces of the heat roller and the press roller are formed of a releasing resin such as, for example, a fluorine resin, and a releasing liquid is not substantially supplied to the surfaces.
Furthermore, as the invention for solving the above-described problems, the following aspects are preferred.
That is, the 5th aspect of the invention is the toner for developing the electrostatic latent image described in the 1st or 2nd aspect described above. The binder resin is composed of at least two kinds of a binder resin (A) and a binder resin (B), the weight average molecular weight (Mw) of the binder resin (A) is from 8000 to 18000, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the binder resin (A) is from 2 to 4, the weight average molecular weight (Mw) of the binder resin (B) is from 20,000 to 40,000, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the binder resin (B) is from 3 to 5.
The 6th aspect of the invention is the toner for developing the electrostatic latent image described in one of the 1st, 2nd, and 5th aspects described above. The toner is prepared by a melt kneading method.
The 7th aspect of the invention is the toner for developing the electrostatic latent image described in one of the 1st, 2nd, 5th, and 6th aspects. The binder resin is polyester.
The 8th aspect of the invention is the toner for developing the electrostatic latent image described in one of the 1st, 2nd, 5th to 7th aspects described above. The toner is a color toner.
The 9th aspect of the invention is the toner for developing the electrostatic latent image described in one of the 1st, 2nd, 5th to 8th aspects described above. The wax has a melting point in the temperature range of from 70 to 100xc2x0 C., a melt viscosity of from 1 to 200 mPaxc2x7s at 110xc2x0 C., and the content thereof to the toner is from 5 to 10% by weight.
The 10th aspect of the invention is the toner for developing the electrostatic latent image described in the 1st, 2nd, 5th to 9th aspects described above. The toner contains inorganic fine particles in an amount from 1 to 10% by weight to the toner.
The 11th aspect of the invention is the image-forming process described in the aspect 4 described above. When the toner amount on the recording paper is 0.50 mg/cm2 and the glossiness (75 degree gloss) is from 40 to 60, and preferably 40 to 50.
The 12th aspect of the invention is the image-forming process described in the 4th or 11th aspect described above. The surface temperature of the heat roller and the press roller is from 150 to 180xc2x0 C.
The 13th aspect of the invention is the image-forming process described in one of the 4th, 11th, and 12th aspects described above. The peripheral speed of the heat roller and the press roller is from 70 to 120 mm/second.
The 14th aspect of the invention is the image-forming process described in one of the 4th, and 11th to 13th aspects described above. The rubber hardness of the heat roller and the press roller is from 55 to 85 degrees by Asker C and the pressing force of the heat roller and the press roller is from 392 to 638N.
The 15th aspect of the invention is the image-forming process described in one of the 4th and 11th to 14th aspects described above. Each of the heat roller and the press roller has an elastic layer and a surface layer on the core surface in the order and the rubber hardness of the elastic layer is from 10 to 40 degrees by Asker C.